Global Seafloor Survey Reveals Volcanic Wonderland

In this marine gravity model of the North Atlantic, red dots show locations of earthquakes with magnitude above 5.5 and highlight the present-day location of seafloor spreading ridges and transform faults. This gravity information shows the details of the plate tectonic history of the rifting of these continents, including the subtle signatures of fracture zones that are currently buried by sediment.David Sandwell / Scripps Inst. of Oceanography / UCSD

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A new topographic map of Earth's mysterious ocean floor reveals thousands of towering volcanoes, hidden gashes where supercontinents ripped apart and other never-before-seen features once veiled by miles of water and thick sediment.

The topography of Earth's seafloor is as corrugated and bumpy as a book set in Braille. By reading these peaks and ridges, scientists can chronicle the birth of new ocean crust and the past wanderings of Earth's continents.

However, even though the seafloor carries the pivotal clues to plate tectonics, the dry surface of Mars has been detailed more clearly than the ocean's watery depths.

The seafloor topography comes from a gravity model of the ocean, which is in turn based on altimetry from the Jason-1 and Cryosat-2 satellites.

Altimetry measures sea surface height from space by timing how long it takes a radar signal to reflect off the ocean and return. The ocean surface has subtle highs and lows that mimic both seafloor topography and Earth's gravity field.

The results represent "a breakthrough in space-based marine gravity observation," Cheinway Hwang, who was not involved in the study, wrote in a commentary accompanying the report. Hwang is a professor at National Chiao Tung University in Hsinchu, Taiwan.

The world's volcano count jumped tremendously thanks to the new map. The number of seamounts soared from around 5,000 to about 20,000, Sandwell said. Seamounts are small, conical volcanoes that are usually inactive or extinct. In the deep ocean, tall seamounts attract a riot of marine life. The map captures all seamounts more than 0.9 miles (1.5 kilometers) tall.